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5 IV. IMPACTS OF THE PREFERRED ALTERNATIVE CHANGES Only two criteria of the preferred alternative (the upramp rate limit and the maximum flow) were changed between the draft and final EIS. The maximum daily change in flow, minimum flow, and the down ramp rate criteria were not changed. Changes to the maximum flow and upramp rate criteria would have no effect on the monthly release volumes. Use of the increased upramp is expected to occur almost every day. Use of the increased maximum flow criteria would be infrequent especially during minimum release years because the maximum flow criterion would often be over ridden by the monthly release volume and the maximum allowable daily change criterion. No linkage was found between upramp limits and negative effects to the physical or biological resources of Glen and Grand Canyons. Since use of the increased maximum flow criteria would be infrequent, differential impacts were judged to be insignificant based on impact analyses of other EIS alternatives. It should be noted that in high and medium release volume years the potential for extended periods of 20,000 to 25,000 cfs flows would be quite likely; especially during the summer and winter seasons when release volumes are high. This is unchanged from the draft EIS. A. Increasinq the Uoramo Rate A range of research flows was conducted from June 1990 through July 1991 as part of the GCES Phase II program. These included high (3,000 cfs to 19,000 cfs) and low (3,000 cfs to 10,000 cfs) fluctuating flows with fast (about 7,000 cfs/hour) and slow (about 3,200 cfs/hour) up and down ramp rates. There were also several approximately steady flow periods during which the ramp rates were less than 1,000 cfs/hour. GCES Phase II identified cause and effect relationships between the range of fluctuations (and downramp rates) and adverse impacts to canyon resources. However, no cause and effect relationships between upramp rates and adverse impacts to canyon resources were identified. The draft EIS (a public document peer reviewed by GCES, the National Research Council, and the EIS Cooperating Agencies) states on page 95 that up ramp rates have not been linked to sandbar erosion. The draft EIS also states on page 190 that "Rapid increases in river stage would have little or no effect on sandbars." Based on work completed by Budhu and Gobin (1994), C1uer and Dexter (1994) and the U.S. Geological Survey (Carpenter, et. a1., 1995) it was determined that the upramp rate would have no imoact on the erosion of the beaches. This conclusion was based on: 1. The down ramp has been shown to be the primary controlling factor in beach erosion (Budhu and Gobin, 1994). The downramp would remain the same (1,500 cfs/hr) and therefore the upramp should not cause any concern for beach erosion.